Dna Identification

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DNA IDENTIFICATION

K GOPI



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HOW IS A DNA PROFILE

PRODUCED?

• DNA strands chopped into fragments

• By restriction endonucleases

• Cut DNA at intron sequences (region of thechromosome used for DNA profilling)

• Many restriction enzymes; specific for

recognition sites



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PRODUCED?

• Mini-satelite : 20-50 base sequence

repeated for 50-100 times

• Micro-satelite : 2-4 base sequence repeatedfor 5-15 times

• Restriction enzymes cut the both repeated

units leaving a mixture of mini and microsatelite



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PRODUCED?

• The fragments are separated and identified

• Gel electrophoresis



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GEL ELECTROPHORESIS

• A variation of chromatography

• DNA fragments placed in wells in agarose gel

medium• The medium is buffered to maintain a constant pH

• Known DNA fragments are added to aid the

identification

• The gel medium contains dye ex: ethidium

bromide which binds to the DNA fragments



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GEL ELECTROPHORESIS

• The dye will give fluorescence effect if placedunder UV light

• DNA bands formed

• DNA samples also added with the dye- do not bind but moves faster than DNA so that currentcan be turned off before samples run out

•DNA fragments moves towards the positive anode• Phosphate group negatively charged

• Different rate of movement (mass and charge)



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GEL ELECTROPHORESIS

• Needs large sample of DNA

• Minimum 50 base pairs-mini satelites

• Looks like supermarket barcode

• Smaller region can be identified by using

the extension of the method



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SOUTHERN BLOTTING

• Alkaline buffer added (denaturates DNA and

exposing the base sequences)

• Nylon filter or nitrocellulose paper is placedover it

• Dry absorbent paper is used to draw the DNA

fragments from gel to filter

• Leaving as blots on the filter



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REVIEW OF THE PROCESS

AGAINStage 1:

• Cells are broken down

to release DNA• If only a small amount

of DNA is available,

amplified using the

polymerase chainreaction (PCR)



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AGAINStep 2:

• The DNA is cut into

fragments usingrestriction enzymes.

• Each restriction enzyme

cuts DNA at a specific

base sequence.



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AGAIN• The sections of DNA that are cut out are called

restriction fragments.

• This yields thousands of restriction fragmentsof all different sizes because the basesequences being cut may be far apart (long

fragment) or close together (short fragment).



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AGAINStage 3:

• Fragments are separated on the

basis of size using a process called

gel electrophoresis.• DNA fragments are injected into

wells and an electric current is

applied along the gel.



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AGAIN• DNA is negatively charged

so it is attracted to the

positive end of the gel.

• The shorter DNA fragments

move faster than the longer

fragments.

• DNA is separated on basisof size and charge.



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AGAIN• A radioactive material is

added which combines

with the DNA fragments

to produce a fluorescent

image.

• A photographic copy of

the DNA bands isobtained.



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AGAINStage 4:

• The pattern of fragment distribution is then

analysed.



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USES OF DNA PROFILING

• DNA profiling is

used to solve

crimes and medicalproblems



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CRIME

• Forensic science is the use of scientific

knowledge in legal situations.

• The DNA profile of each individual ishighly specific.

• The chances of two people having exactly

the same DNA profile is 30,000 million to 1(except for identical twins).



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BIOLOGICAL MATERIALS USED

• Blood

• Hair

• Saliva

• Semen

• Body tissue cells

• DNA samples have been

obtained from vaginalcells transferred to theoutside of a condomduring sexual intercourse



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SOLVING CRIMES

• The pattern of the DNA profile is then compared

with those of the victim and the suspect.

•If the profile matches the suspect it providesstrong evidence that the suspect was present at the

crime scene

• it does not prove they committed the crime

• If the profile doesn’t match the suspect then thatsuspect may be eliminated from the enquiry



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EXAMPLE

• A violent murder occurred.

• The forensics team retrieved a blood sample

from the crime scene.• They prepared DNA profiles of the blood

sample, the victim and a suspect as follows:



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WAS THE SUSPECT AT THE

CRIME SCENE?SuspectsProfile

Blood samplefrom crimescene

Victimsprofile



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SOLVING MEDICAL PROBLEMS

DNA profiles can be used to determine whether a

particular person is the parent of a child.

A childs paternity (father) and maternity (mother) can

be determined.

This information can be used in:

• Paternity suits

• Inheritance cases• Immigration cases



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EXAMPLE: A PATERNITY TEST

• By comparing the DNA profile of a

mother and her child it is possible to

identify DNA fragments in the child

which are absent from the mother and

must therefore have been inherited

from the biological father.



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IS THIS MAN THE FATHER OF

THE CHILD?

Mother Child Man



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INTERESTING CASE

• Helena Greenwood was a biochemist

working on DNA analysis in US

• In 1984, David Frediani broke into her home and held her at gunpoint for several

hours and sexually assaulted her

• She persuaded him not to kill her by tellinghim that she would not tell anyone



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INTERESTING CASE

• But she gave the description to the police and

eventually the found David

• He was granted bail and set for trial in 1985

• Helena and her husband Roger moved to San

Diego

• But 3 weeks before the trial, Roger found Helena

dead in their garden strangled and beaten

• WHO WAS THE PRIME SUSPECT?



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INTERESTING CASE

• Evidence from credit card showed that

David had been in the area just before the

murder but no forensic evidence linkinghim to Helena’s body

• David stood for the original trial and was

imprisoned for 3 years



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INTERESTING CASE

• In 1999, the San Diego police reopened anumber of unsolved cases

• To see PCR and DNA profiling help to solvethem

• Skin fragments beneath her fingernails foundDNA fingerprint matched David

• After 15 years, he was sent for lifeimprisonment



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MINI TEST

1. Explain how protein is synthesised

2. Explain how DNA profiling is done

3. List evidences that can be used to suggest evolution

4. Differentiate genetic flow and genetic drift

5. What is natural selection?

6. List types of natural selection and their examples

7. Draw the graphical illustration on types of natural selection

8. What is speciation?

9. Describe about types of reproduction isolation.

Dna Identification

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